Group transmissions and dual clutch transmissions are known transmission types. Moreover, group transmissions that comprise a dual clutch are also known.
Group, or multi-group transmissions have the advantages that by combining two or three transmission groups they provide a large number of gears, they operate efficiently, and with regard to their number of gears they can be produced in a structurally compact form. However, in common with all manual or automated variable-speed transmissions they are inherently associated with an interruption of the traction force. In contrast, dual clutch transmissions have the advantage that over a sequential series of shifts, in which in each case a gear associated with one of the clutches is active while a connection gear associated with the other clutch has been preselected, they can basically be power-shifted, i.e. they enable gearshifts that are largely free from traction force interruption and therefore provide a high level of driving comfort.
Accordingly a combination of both transmission types seems appropriate, particularly in commercial vehicles such as long-haul trucks, which must have, on the one hand, a large number of gears with a corresponding transmission spread and, on the other hand, a high level of driving comfort along with high operational reliability. However, in transmissions designed in such manner not all the gears can necessarily be power-shifted. When, as is usual, the group transmission has an input or splitter group and a main group of countershaft configuration as well as a downstream range group of planetary design, such that the range group can be shifted between two gear ranges, then it is true that in accordance with the torque flow of the successive gears most of the gears within the two gear ranges can, with the help of the dual clutch, be made as power-shifting gears. However, the shifting process of the range group itself is as a rule not traction-force-supported. Since in addition the shifting process lasts a comparatively long time, this is regularly sensed by the driver and perceived as annoying.
In the not previously published DE 10 2008 054 477 A1 by the present applicant a multi-group transmission is proposed, which enables traction-force-supported gearshifts. This multi-group transmission has an input-side splitter group with three gear constants, a three-gear main group and a downstream range group. The splitter group and the main group are configured in a space-saving and load-distribution-balanced manner with two common, axis-parallel countershafts. The range group is formed as a planetary transmission with a central sun gear, a planetary gearset guided by a planetary carrier and an outer ring gear. By means of a starting clutch a transmission input shaft can be connected at one end to a driveshaft of a drive motor. At its other end the transmission input shaft can be directly connected by means of a shifting element, i.e. without branching via the countershafts, to a main transmission shaft arranged axially behind it. At its output end the main transmission shaft is connected fixed to the sun gear of the range group. Furthermore, a power-shift clutch is provided, by means of which a loose wheel mounted to rotate on the transmission input shaft and belonging to the first gear constant nearest to the motor can be connected to the drive input shaft, so that the power-shift clutch bridges across the starting clutch. The starting clutch and the power-shift clutch can for example be made as a dual clutch whose common clutch cage is connected to the drive input shaft.
Thanks to the fact that the first input constant can be engaged regardless of the shift condition of the starting clutch, and to the possibility of connecting the transmission input shaft directly to the main transmission shaft, it is possible to select at one and the same time a direct and a branched power path and by means of an overlapping opening and closing of the two clutches, to have one merge into the other in the drive-power flow. It is true that in this way a number of powered gearshifts are possible with this transmission. However, a shift of the downstream range group between a lower gear range stepped down by the planetary transmission and an upper gear range not stepped down due to blocking of the planetary transmission, is not traction-force-supported.
From DE 10 2008 001 200 A1 another traction-force supporting multi-group transmission with a splitter group, a main group and a range group as well as a dual clutch is known. In this case one clutch is used as a starting clutch to connect a driveshaft of a drive motor to a transmission input shaft and the other clutch is used as a power-shift clutch for engaging an intermediate gear by connecting the driveshaft with a main transmission shaft that passes through the transmission groups. The transmission input shaft is in the form of a hollow shaft arranged coaxially over the main transmission shaft. During a gearset the power-shift clutch is closed and thereby an intermediate gear is engaged, without disengaging the starting clutch. By virtue of the direct connection of the driveshaft to the main transmission shaft, the intermediate gear corresponds to the direct gear of the splitter group and the main group. In this case the power-shift clutch operating with slip supports the motor torque at the drive output of the vehicle, whereby the motor speed is synchronized. Due to the torque support a break in traction-force during a neutral setting of the splitter group and/or the main group during a change from the original gear to the target gear, is prevented.
If in the usual way the main transmission shaft is connected at its output-side end directly to a sun gear of the range group but only indirectly to a transmission output shaft at the output of the range group, then during a shift of the range group in which the force flow changes, for example, between a coupling of a ring gear to a housing and a coupling of the ring gear to a transmission output shaft connected to a planetary carrier, the intermediate gear cannot provide any traction-force support. In this connection DE 10 2008 001 200 A1 proposes a means of assistance in that the main transmission has an additional hollow shaft which is arranged coaxially on the main shaft and on which the loose wheels and associated shifting elements of the main transmission are arranged. Instead of the main transmission shaft, it is this hollow shaft which at its output-side end is connected to the sun gear, whereas the main transmission shaft passes uncoupled through the range group and is connected directly to the transmission output shaft. Thus, range shifts can also be traction-force-supported by temporary engagement of the direct gear of the transmission as a whole as an intermediate gear during a gearshift. However, the range group itself can still not be power-shifted. Accordingly, in transmission designs that do not provide for any intermediate gear engagement, the range shift is again not traction-force-supported. Furthermore, the hollow shaft that extends as far as the sun gear is relatively long, so the mounting of the very long main transmission shaft passing through the hollow shaft and extending from the starting clutch to the transmission output, rather falls short of optimum.